Dragonfly Nymph Tri-leaflet Valve

A dragonfly nymphs create (a) straight jets for jet propulsion and (b) deflected jets for breathing. Colors show the flow streaks/time evolution of fluid particles in the jet stream. Insets in the top left hand corners show the corresponding valve configuration.

A dragonfly nymphs create (a) straight jets for jet propulsion and (b) deflected jets for breathing. Colors show the flow streaks/time evolution of fluid particles in the jet stream. Insets in the top left hand corners show the corresponding valve configuration.

The aquatic Anisopteran dragonfly larva possesses a modified hindgut pump that enables jet propelled locomotion and respiration. The flows associated with these functions are modulated by a tri-leaflet anal valve. Previous studies of this valve have been limited to showing the larva’s ability to modulate the aperture size through concurrent movement of the three leaflets. However, we have newly observed that the dragonfly nymph’s anal valve is capable of more sophisticated movements by actually independently controlling each of the leaflets.

A cross-section of the dragonfly nymph's hindgut.

A cross-section of the dragonfly nymph's hindgut.

The impact of this unique feature on the two functions of the pump is being investigated through simultaneous visualization of the dragonfly’s valve kinematics and the resulting jets. Our results indicate that by controlling the individual anal valve leaflets, the larva directs its propulsion jet straight using a symmetric nozzle opening (fig. a), while diagonally deflecting its respiratory jet when using an asymmetric nozzle opening (fig. b). The straight jet appears to reduce the thrust loss during propulsion due to side-thrust generation, while the deflected jet seems to induce a secondary entrainment flow during respiration that is favorable to clean and efficient breathing.